As a multilayer printed board, there is a type provided with a differential signal wiring. In the multilayer printed board, portions of a differential signal wiring formed on one side are connected to portions of the differential signal wiring formed on the other side through vias. The differential signal wiring needs to be configured such that signals are transmitted with the same phase and reverse polarities from a transmission end and are received with a phase shift within a predetermined range by a reception end. For this reason, there is conventionally proposed a technique of adjusting the electric lengths of a differential signal wiring on a printed board. For example, the shapes of vias are altered from a circular shape to an elliptical shape, and/or the land diameters of vias are made different, to adjust the electric lengths of the differential signal wiring.
However, according to the conventional method, the shapes of vias or lands are made different depending on the place, and so the shapes of vias or lands are varied depending on the differential signal wiring. Consequently, it takes labor hour to design the layout.